Removal of atmospheric pollutants from gas, related apparatuses, processes and uses thereof

ABSTRACT

One aspect of the invention relates to a method comprising a single-stage conversion of an atmospheric pollutant, such as NO, NO 2  and/or SO x  in a first stream to one or more mineral acids and/or salts thereof by reacting with nonionic gas phase chlorine dioxide (ClO 2   0 ), wherein the reaction is carried out in the gas phase. Another aspect of the invention relates to a method comprising first adjusting the atmospheric pollutant concentrations in a first stream to a molar ratio of about 1:1, and then reacting with an aqueous metal hydroxide solution (MOH). Another aspect of the invention relates to an apparatus that can be used to carry out the methods disclosed herein. The methods disclosed herein are unexpectedly efficient and cost effective, and can be applied to a stream comprising high concentration and large volume of atmospheric pollutants.

CROSS REFERENCE TO RELATED APPLICATIONS

The present invention is a continuation of U.S. patent application Ser.No. 14/684,948, filed Apr. 13, 2015, which is a divisional of Ser. No.13/727,512, filed Dec. 26, 2012, both of which claim priority to U.S.Provisional Application No. 61/584,347, filed Jan. 9, 2012, and U.S.Provisional Application No. 61/656,192, filed Jun. 6, 2012, all of whichare incorporated herein by reference, including drawings.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The field of the invention relates to a method for the removal ofatmospheric pollutants from a gas stream, and related apparatus,processes and uses thereof.

2. Description of the Background

Atmospheric pollutants are those gases, particles, radicals and othermolecules that make their way into the atmosphere from other sources orform in the atmosphere from the chemical reactions of other moleculesand energy sources. In general, atmospheric pollutants can damage theatmosphere by contributing to the “greenhouse effect,” by breaking downthe ozone layer, or by contributing to incidents of asthma and breathingproblems. These pollutants are not merely confined to the outside, butcan also be found in buildings. For example, many buildings have loadingdocks near the air intake system. When a truck pulls up to the loadingdock, the truck exhaust can be pulled into the air intake system for abuilding and pollute the indoor air. There are also sources ofatmospheric pollutants that originate from materials inside a building,such as carpet, paint, and commonly used chemicals.

Oxides of nitrogen are a group of six compounds. Two members of thisgroup: nitrogen monoxide (NO) and nitrogen dioxide (NO₂), togetherreferred to as NO_(x) hereinafter, are reactive species that areimportant because they are problematic atmospheric pollutants andsubject to regulatory control. The gases are regulated because of thelarge quantities produced through combustion and other chemicalreactions and because of their adverse effects in atmospheric chemistry.More than 2 million tons of NO_(x) were generated within the UnitedStates in 2011. Combustion typically produces 95% NO and 5% NO₂.Nitrogen monoxide, NO, is a significant reactive species in anatmospheric system, along with being present in several types of wastegases. It is the key component in the chain oxidation of organics, whichis brought about initially by the radical product of the reaction ofhydroxyl radical with organic compounds then adding an ozone molecule tothe open radical site. NO scavenges an oxygen atom from the radicalorganic species to form NO₂. In ambient air, there are other importantmechanisms by which NO is quickly converted to NO₂.

2NO+O₂→NO₂

K^(298K)=2.0×10⁻³⁸ cm⁶ molecule⁻²s⁻¹

RO₂+NO→RO+NO₂

K^(298K)=7.6×10⁻¹² cm⁶ molecule⁻²s⁻¹

HO₂+NO→OH+NO₂

K^(298K)=8.3×10⁻¹² cm⁶ molecule⁻²s⁻¹

NO+NO₃→NO₂+₂

K^(298K)=1.8×10⁻¹⁴ cm⁶ molecule⁻²s⁻¹

NO+NO₃→2NO₂

K^(298K)=3.0×10⁻¹¹ cm⁶ molecule⁻²s⁻¹

Alternative NO_(x) Treatment Methodology

Current methods of cleaning air, such as catalytic oxidation,condensation, absorption, and carbon bed adsorption, are in generalbulky, expensive, and maintenance intensive. Therefore, a process thatcould address at least one of these problems found with the currentlyused methods would be a beneficial next step in the development ofbetter technology for air quality control. An ideal process can controlboth low and high concentrations of NO_(x) in the air to be treated.

Carbon Bed Adsorption

Carbon bed adsorption, or adsorption by another material, is a processthat does not convert the components of waste gases to other compoundsas part of the process. Adsorption is an effective way of reducing theconcentration of components in a waste gas stream to a low concentrationthrough attachment to a substrate.

The contaminated gas flows through the bed, where the components of thewaste gas can be adsorbed onto the bed material. There are, however,several problems with granular bed adsorption. First, the choice of thebed material is one of the critical factors in the success of thecomponent removal. Activated carbon, molecular sieves, activatedalumina, and activated silica are common bed materials, althoughactivated carbon is commercially the material of choice. The compositionof the bed material influences which waste gas components will beadsorbed and which components will sneak through the system and into theoutlet air stream. Therefore, it is helpful if the operator knows thecontaminants of the air sample that is being cleaned.

Second, the adsorption technique does not break down the components ofthe waste gas into smaller and/or other compounds; it only collects themon the bed material. Once the bed becomes saturated, it must be takenoff line and cleaned or replaced. The cleaning process can involvesimply steam cleaning the bed, called regeneration, or can involve usinga solvent combined with steam cleaning to remove captured waste gascomponents. The waste products from this process must then be collectedand disposed of by an environmentally safe procedure. The most commonprocedure is to separate the waste gas components from the aqueous phasethat was produced by the steam cleaning process. This is time consuming,labor intensive and costly.

Another problem with the adsorption technique is that it requires morethan one bed in parallel and sometimes in series. The adsorption processrequires beds in parallel so that when one bed becomes saturated, it canbe taken off line and the other bed is put into subsequent use.Sometimes, it becomes advantageous to put beds in series so that largeconcentrations of waste gas components can be removed. The operator canalso put beds made of different materials in series to target differentcombinations of waste gases. These adsorption beds are quite bulky,since their average depth is one to three feet, therefore this processcan be undesirable if space is limited. The arrangement of beds inseries and parallel add to the consumption of time, labor and money incooling and cleaning of the waste and the bed material.

Absorption

Absorption is the process by which part of a gas mixture is transferredto a liquid based on the preferential solubility of the gas in theliquid. This process is used most often to remove acid stack gases, butit is a complex and costly method of control and often includes theadded cost and inconvenience associated with the removal of otherinnocuous components of waste gases. The high cost of the process isbased on the choice of the absorbent and the choice of the strippingagent. Absorption is limited in its utility and not widely implementedin small industrial settings.

Electrical Discharges

Plasmas are electrical discharges that form between electrodes. Thereare five general classes of non-equilibrium plasmas that can be used insome capacity for chemical processing, including synthesis anddecomposition: the glow discharge, the silent discharge, the RFdischarge, the microwave discharge, and the corona discharge. Each classis specific based on the mechanism used for its generation, the range ofpressure that is applicable during its use, and the electrode geometry.

While electrical discharges are effective in breaking down components ofwaste gases into other compounds and components, they require powersources (in some cases a significant one), may not be able to handleindustrial scale treatment without honeycombed and serial designs of thedischarges, and are generally designed to combat complicated waste gasstreams that comprise various components, including ozone, NO_(x) andvolatile organic compounds.

Wet Scrubbing

For waste gas streams that contain a significant amount of NO_(x),whether it is an original contaminant or the result of chemicalconversion of a volatile organic component, conventional technologies,such as those described earlier, may not be able to efficiently handlethe NO load on an industrial scale. Wet scrubbing technologies canhandle waste gas streams with significant amounts of NO_(x).Conventional wet scrubbing technologies for industrial scale NO_(x)treatment typically treat the NO_(x) with two, three or more-stage wetscrubbing systems. The most common currently used is a three-stageprocess: Stage 1 converts NO into NO₂. Stage 2 chemically transforms theNO₂ into other nitrogen containing compounds. Stage 3 removes odorscreated in the second stage. Literature shows a number of chemicalreactants, some of which are outlined herein, that are utilized in thisand other multi-stage NO_(x) treatment technologies. These includenitric acid and hydrogen peroxide; sodium hydrosulfide and sodiumhydroxide, hydrogen peroxide, ozone gas, sodium chlorite solution; andferric salt solutions and others. All of these have pronouncedlimitations in operating costs, equipment costs or removal efficiencies.

Some prior art references have confusingly described the scrubbing agentused in wet scrubbing wherein sodium chlorite is dissolved in water, aschlorine dioxide when it is actually chlorite, the anionic (ClO₂ ¹) formof the ClO₂ molecule that is used in the wet scrubbing process. Thisdistinction is made because the anionic (ClO₂)⁻¹ chlorite and theneutral (ClO₂)⁰ chlorine dioxide have different chemicalcharacteristics. These differences provide the embodiments of thepresent disclosures unexpected advantages over the wet scrubbingtechnology typically described in literature.

For example, U.S. Pat. No. 7,455,820 to Lee et al. describes the use ofchlorine dioxide (ClO₂)⁰ in NOx and SOx reactions. However, Lee '820clearly teaches that the reactions described in equations (4) & (5) ofthat disclosure occur in a liquid phase within a reaction vessel knownas a “bubbling reactor” (see Lee FIG. 1), and thus these reactions occurin a liquid phase, and not in a gas/mist phase reaction environment.

Catalytic Reactions

Catalysts that can reduce NO_(x) into innocuous nitrogen compounds areeffective on NO_(x) waste gas streams with low oxygen concentrations,temperatures between 230° C. and 350° C., devoid of heavy metals thatpoison the catalyst and sulfur compounds that tend to interfere with thecatalysts. However, most industrially produced NO_(x) waste gas streamsdo not meet these requirements. Thus, the catalyst technology is notapplicable.

To this end, it would be desirable to develop a method that convertsNO_(x) in a waste gas stream, and the related apparatus and processesthereof, wherein some embodiments of the method, apparatus, and/orprocess, when compared to certain known technologies, achieves at leastone of the following goals: a) can operate on an industrial scale, b)requires less significant amount of energy from outside sources, c) canprocess waste gases in the gas phase with low, medium and/or highamounts of humidity (including liquid and/or aqueous phase materials),d) can process waste gases using a liquid stream (e.g. an aqueousstream), e) can treat waste gases containing sulfur, sodium and/or othermetal containing compounds f) is more cost efficient relative to thescale of the process g) is easier to install and operate, and h) caneffectively operate as a single-stage or two-stage unit.

SUMMARY OF THE INVENTION

One aspect of the invention relates to a first method for converting oneor more oxides of nitrogen, and/or one or more oxides of sulfur (i.e.,atmospheric pollutants) in a first stream to one or more mineral acidsand/or salts thereof, as a result of contacting the first stream with asecond stream comprising nonionic chlorine dioxide)(ClO₂ ⁰) in the gasphase as defined below.

In one embodiment, the second stream comprises a mist stream, liquidstream or a combination thereof wherein ClO₂ ⁰ is adsorbed, suspendedand/or dissolved in a liquid composition. The second stream may beintroduced into the reaction chamber using an atomizer to produce gasphase ClO₂ ⁰ to react with the atmospheric pollutants. In certainembodiments, the second stream further comprises a gas stream comprisingClO₂ ⁰.

In another embodiment, a method of removing atmospheric pollutioncompounds from a waste gas stream disclosed herein comprises: providinga single-stage air scrubbing apparatus, providing a waste gas stream (afirst stream) having at least one atmospheric pollution compound (e.g.one or more oxides of nitrogen and/or one or more oxides of sulfur),providing at least one additional gas stream, mist stream, liquid streamor combination thereof (a second stream), introducing the first streamand the second stream into the single-stage air scrubbing apparatus at aflow rate and retention time in the reaction vessel that is sufficientto allow for conversion of at least one atmospheric pollution compoundvia a gas phase reaction.

Another aspect of the invention relates to a second method comprising:

(2a) contacting a first stream comprising NO and/or NO₂ with a secondstream comprising ClO₂ ⁰ to provide a third stream comprising NO and NO₂at a molar ratio of about 1:1; and

(2b) contacting the third stream with a fourth stream comprising anaqueous metal hydroxide (MOH) solution that contains a reaction promoterselected from the group comprising NaOCl, H₂O₂, KMnO₄, O₃, NaClO₂,NaClO₃, CaOCl and combinations thereof in a concentration by weight ofabout 2% to 6% to convert NO and NO₂ to MNO₂.

In one embodiment, a method of removing atmospheric pollution compoundsfrom a waste gas steam disclosed herein comprises: providing a two-stageair scrubbing apparatus, providing a waste gas stream (a first stream)having at least one atmospheric pollution compound (e.g. one or moreoxides of nitrogen and/or one or more oxides of sulfur), providing atleast one additional gas stream comprising ClO₂ ^(O) adsorbed, suspendedand or dissolved in a liquid or a combination thereof and/or ClO₂ ^(O)gas (a second stream) into the first stage of the air scrubbingapparatus at a flow rate and retention time that is sufficient to allowmixing of a first stream comprising NO and/or NO₂ with a second streamcomprising ClO₂ ⁰ to provide a third stream comprising NO and NO₂ at amolar ratio of about 1:1. This third stream gas mixture is thenintroduced into a second reaction apparatus at a flow rate and retentiontime that is sufficient to allow mixing of the third stream with afourth stream comprising an aqueous metal hydroxide (MOH) solution thatcontains a reaction promoter selected from the group comprising NaOCl,H₂O₂, KMnO₄, O₃, NaClO₂, NaClO₃, CaOCl and combinations thereof in aconcentration by weight of about 2% to 6% to convert NO and NO₂ to MNO₂.

In another embodiment, a method of removing atmospheric pollutioncompounds from a waste gas stream disclosed herein comprises: providinga two-stage air scrubbing apparatus, providing a waste gas stream (afirst stream) having at least one atmospheric pollution compound (e.g.one or more oxides of nitrogen and/or one or more oxides of sulfur),providing at least two additional gas streams, mist streams, liquidstreams or combination thereof (a second stream and a fourth stream),introducing the first stream and the second and fourth streams into thetwo-stage air scrubbing apparatus at a flow rate and retention time inthe reaction vessels that are sufficient to allow for conversion of atleast one atmospheric pollution compound in a gas phase reaction.

Another aspect of the invention relates to an apparatus that can be usedin the methods disclosed herein.

In one embodiment a single-stage air scrubbing apparatus is disclosedthat includes: at least one reaction vessel having a first end, a secondend, an enclosure, comprising at least one wall, a volume withinenclosure and a residence time component, at least one introduction ductthat is coupled to the reaction vessel, and a turbulence component;wherein the residence time component is sufficient to allow theconversion of at least one atmospheric pollution compound. In someembodiments, the at least one atmospheric pollution compound comprisesone or more oxides of nitrogen, one or more oxides of sulfur or acombination thereof.

Another embodiment discloses a two stage air scrubbing apparatusincluding at least one reaction vessel for each stage.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1: Chlorine dioxide's tendency to decompose as a function ofchlorine dioxide concentration in air (Practical Chlorine Dioxide,Volume 1, Greg. D. Simpson, PhD, Copyright ©2005, pg 12, section titled“Properties of Chlorine Dioxide;” and the OxyChem Technical Data Sheet,Chlorine Dioxide Safety & Handling, titled Partial Pressures vs. ClO₂Concentration).

FIG. 2: Induction time of chlorine dioxide, the time required fordecomposition of chlorine dioxide, as a function of time, partialpressure, and temperature.

FIG. 3: Chlorine dioxide vapor pressure as percent in air at varioustemperatures.

FIG. 4: An apparatus used to perform a single-stage method describedherein according to one embodiment.

FIG. 5: A flow diagram for an embodiment of a two-stage method describedherein.

DETAILED DESCRIPTION

There are three forms of ClO₂, the neutrally charged (ClO₂ ⁰), the anioncarrying a negative charge (ClO₂ ¹) and the cation carrying a positivecharge (ClO₂ ⁺). Although all the three forms are often referred to asClO₂ or chlorine dioxide in the literature, each has a different name(Table A) and different chemical characteristics.

TABLE A (ClO₂)⁰, (ClO₂)⁻, and (ClO₂)⁺ Formula used Preferred IUPACConventional in the present Name Ionic charge Formula disclosureChlorine dioxide 0 ClO₂ (ClO₂)⁰ Chlorite −1 ClO₂ ⁻ (ClO₂)⁻ Chloryl +1ClO₂ ⁺ (ClO₂)⁺

Chlorine dioxide can be used to convert NO into NO₂, typically in a wetscrubbing apparatus, according to reaction (1) below.

2NO+ClO₂+H₂O→NO₂+HNO₃+HCl  (1)

The use of sodium chlorite in water solution within a packed bed, traytype scrubbing, or other wet scrubbing apparatus to convert NO₂ intonitric acid, is described in reaction (2) below.

4NO₂+NaClO₂+2H₂O→4HNO₃+NaCl  (2)

Reactions (1) and (2) are typically described in wet scrubbing reactionsusing chlorite salts in aqueous solutions. Wet scrubbing methods utilizeClO₂ ⁻ provided from the dissociation of the chlorite salts (e.g. sodiumchlorite) in an aqueous environment for wet scrubbing of NO_(x).However, the literature studies frequently inaccurately identify themechanism as described in reaction 1, wherein the chlorine dioxidereactant is inaccurately identified as the neutral ClO₂ (ClO₂ ⁰) ratherthan the correct chlorite ion (ClO₂).

Reactions (1) and (2) are examples of stoichiometry taken fromliterature that inaccurately identify the ionic chlorine dioxidemolecule. In these reactions and other similar ionic reactions, whenClO₂ is depicted it should more accurately be reported as: ClO₂ ⁻. Foradditional clarification, the ClO₂ ⁻ ion may be formed from dissolvingor suspending a chlorite salt (e.g. sodium chlorite (Na ClO₂)) in water.

In several embodiments of the present disclosure and without beinglimited by any theory, the NO_(x) scrubbing undergoes the reactionsdescribed in reactions (3) and (4), set forth below, wherein ClO₂ refersto the neutral non-ionic chlorine dioxide ClO₂ ⁰. Thus, some embodimentsof the present disclosure differ from the known wet scrubbing technologybecause the scrubbing agents are different: in the known wet scrubbingtechnology, the scrubbing agent is the anionic ClO₂ ⁻; while in someembodiments described herein, the scrubbing agent is the neutral ClO₂ ⁰.Furthermore, because the anionic ClO₂ ⁻ and the neutral ClO₂ ⁰ havedifferent chemical characteristics, such differences provide theembodiments of the present disclosure unexpected advantages over theknown wet scrubbing technology.

A reaction vessel for carrying out the herein-described reactions mayinclude a vessel equipped with one or more turbulence inducing devicesconfigured for insertion therein, one or more inlets for introducingeach of the reaction components including the waste gas stream, and oneor more exhaust outlets. Each of the inlets and outlets to and from thereaction vessel may include one or more sensors for measuring variousaspects of the respective inlet or outlet streams such as quantities ofvarious chemicals, temperature, pressure, flow rate, humidity, etc. In apreferred embodiment, the reaction vessel includes a gas flow sensor formeasuring flow rate and other qualities of the waste gas exiting thereaction vessel after the reaction(s) described herein. Turbulenceinducing device or devices may be stationary or moving, and may beplaced at various locations along the process flow, in regular orirregular spacing, such that they adds turbulence or mixing to thevarious gas streams and in various process stages. For example, aturbulence inducing device may add turbulence to the waste gas streambefore the waste gas comes into contact with the chlorine dioxideaccording to the present invention. In addition, a turbulence inducingdevice may be placed in a duct just prior to a point where gas entersthe vessel. Alternatively or in addition, one or more turbulenceinducing devices may be placed at a beginning of the reaction vesseljust after the waste gas enters the reaction vessel.

The reaction vessel may be in the form of one or more various shapesknown in the art for carrying out the types of chemical reactionsdisclosed herein, such as cylindrical, rectangular, etc. In a preferredembodiment, the reaction vessel is cylindrical, the waste gas isintroduced at a side of the cylindrical reaction vessel and tangentiallyaligned with a circumference of the cylindrical reaction vessel, and theturbulence inducing component is located at a position configured toswirl or mix the gas in a duct just prior to a point where the waste gasenters the vessel. In another preferred embodiment, the reaction vesselis rectangular, and the turbulence inducing component is configured tominimize collision between the vessel walls and gas turbulence withinthe reaction vessel when chlorine dioxide is introduced in a mist orliquid phase as described herein.

In addition, a reaction “vessel” according to the present invention mayinclude one or more reaction vessels in series, each for carrying out asingle one of the one or more reaction(s) according to the presentinvention. Turbulence inducing devices for the reaction vessel mayinclude two or more “spirs.” The spinners may be in series, withadjacent spinners having opposite blade orientations to cause turbulencebetween the devices in series. The spinners contemplated herein mayinclude a variety of blade angles, shapes and orientations.Specifically, the spinner may include from 2 to 30 blades, with bladesangled at an angle of between 5 to 85 degrees, but preferably between 5and 45 degrees, more preferably between 5 and 30 degrees, even morepreferably at an angle of between 25 and 30 degrees, and most preferablyat an angle of 30 degrees.

First Method: Single-Stage Conversion of NO_(x)

One aspect of the invention relates to a first method comprisingcontacting a first stream comprising NO and/or NO₂ (together referred toas NO_(x)) with a second stream to convert the NO_(x) in the firststream to one or more mineral acids and/or salts thereof in asingle-stage conversion, wherein:

(1a) the second stream comprises ClO₂ ⁰ adsorbed, suspended and/ordissolved in a liquid composition; and/or

(1b) the second stream comprises a gas stream comprising ClO₂ ⁰.

In certain embodiments, the first stream contacts the second stream atvarying humidities, including at a high relative humidity, at a mediumrelative humidity, or at a low relative humidity.

Without being limited by any theory, in one embodiment, the methoddescribed above involves the following reactions between NO_(x) andnonionic ClO₂ ⁰:

5NO+2(ClO2)⁰+H₂O→NO₂+2HCl  (3)

5NO₂+(ClO₂)⁰+H₂O→5HNO₃+HCl  (4)

Reactions (3) and (4) are different from reactions (1) and (2). Thereactant ClO₂ in reactions (3) and (4) is nonionic chlorinedioxide)(ClO₂ ⁰), while the reactant ClO₂ in reactions (1) and (2) isClO₂ ¹. Reaction (5) describes a method of creating ClO₂:

NaClO₂→Na⁺+(ClO₂)⁻  (5)

Without being limited by any theory, reactions (1) and (2) followdifferent reaction mechanisms from reactions (3) and (4). Reactions (1)and (2) are much slower and reach a lower equilibrium concentration ofproducts (the reactions do not consume all of the reactants). Reactions(3) and (4) produce a higher concentration of products than reactions(1) and (2) do, and therefore use up more reactants. Thus, compared tothe conventional wet scrubbing of NO based on reactions (1) and (2), themethods described herein based on reactions (3) and (4) allow a moreefficient and faster NO_(x) scrubbing. Thus, the methods describedherein can be used in NO scrubbing at an industrial scale, and may alsobe used in NO_(x) scrubbing of gas stream comprising high concentrationNO_(x).

In certain examples, the concentration of NO_(x) treated according toreactions (3) and (4) is about 10 ppmV or higher, about 200 ppmV orhigher, about 20,000 ppmV or higher, about 50,000 ppmV or higher, orabout 60,000 ppmV or higher in the first stream. The possible NO_(x)concentration mixtures in the first stream include any ratio of NO toNO₂; however the ratio is typically about 90% or more NO in industrialand combustion sources. When ClO₂ ⁰ is provided in an excess amount, andthe contact time is about or longer than the required contact time,reactions (3) and (4) produce substantially complete conversion (about95% or higher conversion, about 98% or higher conversion, or about 99%or higher conversion) of NO_(x) to the one or more mineral acids and/orsalts thereof. The required contact time between ClO₂ ⁰ and NO isreferred to as a residence time. The residence time is dependent uponthe efficiency of gas mixing and the form in which ClO₂ ⁰ is introducedinto the reaction. The reaction can occur at any velocity of the firststream.

In certain embodiments, the throughput of the method is unexpectedlyhigh, wherein the velocity of the first stream can be up to about 2,500ft/min, up to about 2,000 ft/min, up to about 1,500 ft/min, or up toabout 1,000 ft/min. The contact time required to substantially completethe conversion of NO_(x) in the first stream to the one or more mineralacids and/or salts thereof is unexpectedly short, e.g., about 3 seconds,about 1.5 seconds or shorter when ClO₂ ⁰ is introduced in a liquid ormist stream and the two streams are combined in a way that produces anideal mixing; or about 0.15 seconds or shorter when ClO₂ ⁰ is introducedin a gas stream and the two streams combine in a way to produce an idealmixing.

The second stream comprising a gas stream, a mist stream, or a liquidstream is combined with the first stream in a way that provides mixing,e.g. by swirl or turbulence. Such swirl or turbulence may be introducedbefore or after the first stream contacts the second stream, and/orduring the contacting thereof. Moreover, such swirl or turbulence may beintroduced in either the first or second streams prior to contactbetween the streams. Such swirl or turbulence may be accomplished byspinning with a mechanical mixing device (e.g. paddles or blades) thatinduces rotation along the longitudinal axis of the first and secondstream flows, by angular orientation of jets that introduce the secondstream into the first stream, or by vibrational methods. In certainembodiments, the streams are introduced by one or more nozzles. Whenthere is more than one nozzle, the nozzles can be spun in the same ordifferent directions. In certain embodiments, the multiple nozzles arespun in opposite directions to optimize mixing and minimize unnecessaryturbulence. In certain embodiments, the chlorine dioxide is introducedinto the waste gas stream at a point just downstream of a point at whichgas is swirled by the turbulence component.

In one embodiment the second stream comprises ClO₂ ⁰ in a gas stream. Inanother embodiment, the second stream comprises ClO₂ ⁰ gas adsorbed,suspended and/or dissolved in a mist stream, a liquid stream or acombination thereof, wherein the liquid evaporates upon introductioninto the reaction vessel via an atomizer prior to contacting the firststream. In another embodiment the second stream comprises ClO₂ ⁰ in agas stream; and ClO₂ ⁰ gas adsorbed, suspended and/or dissolved in amist stream, a liquid stream or a combination thereof, wherein theliquid evaporates upon introduction into the reaction vessel via anatomizer prior to contacting the first stream. In some embodiments thesecond stream is substantially free of the ionic forms of chlorinedioxide.

The liquid composition may be water based (aqueous) or organic based(i.e. comprising one or more organic solvents that do not react withClO₂ ⁰ at a temperature between about 10° C. and about 50° C.). Theliquid composition may be acidic, neutral, about neutral, or basic. Therate of reaction between ClO₂ ⁰ and NO_(x) in a liquid stream or a miststream reaction is dependent upon the Henry's Law constant for thesolubility of ClO₂ ⁰ in the liquid or mist stream, and the othercompound(s) thereof.

For example, the liquid composition may be a basic aqueous solution toprovide higher solubility of ClO₂ ⁰ (e.g. pH of about 9 or higher).Although ClO₂ ⁰ may decompose in a basic aqueous solutions, the ClO₂ ⁰decomposition rate is slower than the reaction rate of reactions (3)and/or (4). Nevertheless, it is desired to limit the time ClO₂ ⁰ isexposed to the basic aqueous solution to minimize ClO₂ ⁰ decomposition.

For example, the second stream may be formed by mixing the basic aqueoussolution and ClO₂ ⁰ gas together right before contacting the firststream. In one example, the basic aqueous solution and ClO₂ ⁰ gas ismixed together before forming the mist stream. In another example, thesecond stream is formed by mixing a mist stream of the basic aqueoussolution with ClO₂ ⁰ gas. In another example, ClO₂ ⁰ contacts the basicaqueous solution for no more than about 2 minutes before, or no morethan about 10 minutes before contacting the first stream.

Even when the aqueous solution is not basic, it is desired to limit thecontact time of ClO₂ ⁰ and the aqueous solution before contacting thefirst stream. In one example, ClO₂ ⁰ contacts the aqueous solution(acidic, neutral or substantially neutral) for no more than two minutes,for no more than about 30 minutes, or for no more than about 48 hoursbefore contacting the first stream. In each case wherein ClO₂ ⁰ issuspended, adsorbed, or dissolved into a liquid stream, the reactionnonetheless is carried out in the gas phase. For example, the aqueoussolution adsorbed, suspended and/or dissolved with ClO₂ ⁰ may beconverted into a mist stream via an atomizer such that the ClO₂ ⁰evaporates to provide gas phase ClO₂ ⁰ before contacting the firststream.

Examples of the aqueous basic solutions include, without limitation,metal hydroxide (MOH) aqueous solutions. As used herein, MOH includes Mhaving single or multiple valences. Examples of MOH include, withoutlimitation, LiOH, NaOH, KOH, Ca(OH)₂, and Ba(OH)₂ MOH, e.g. sodiumhydroxide, may be considerably less expensive than ClO₂ ⁰ and itspresence may reduce the overall chemical cost in the NO_(x) scrubbingmethods described herein. Furthermore, MOH aqueous solutions may beeasier and safer to handle than ClO₂ ⁰.

The liquid stream can be formed by adsorbing, suspending and/ordissolving ClO₂ ⁰ in a liquid composition.

The mist stream can be provided by any methodology for droplet formation(e.g. spray, release or propel), wherein the method provides forevaporation of all or part of the ClO₂ ⁰ prior to contacting the firststream. Preferably, the mist droplets are generated using one ormultiple air atomized nozzle in which air pressure or sonic vibrationprovides the energy to create the small droplets. In certain examples,the mist droplets have a mean diameter of about 200 microns or lower, orabout 100 microns or lower. In certain examples, a swirl or turbulenceis introduced into the combined first and second streams. In certainexamples, the mist stream comprises a mist of the liquid compositionthat contains adsorbed, suspended and/or dissolved ClO₂ ⁰. The liquidcomposition is the same as described supra.

In certain embodiments, the second stream is provided by the followingsteps:

1a-1a) providing ClO₂ ⁰ adsorbed, suspended and/or dissolved in a liquidcomposition; and

1a-1b) spraying the liquid composition adsorbed, suspended and/ordissolved with ClO₂ ⁰ to provide the second stream which evaporatesprior to contact with the first stream.

The liquid composition is described the same as above.

In certain embodiments, the second stream is provided by the followingsteps:

1a-2a) providing ClO₂ ⁰ gas on site;

1a-2b) adsorbing, suspending and/or dissolving ClO₂ ⁰ gas into a liquidcomposition; and

1a-2c) spraying the liquid composition adsorbed, suspended and/ordissolved with ClO₂ ⁰ gas to provide the second stream which evaporatesprior to contact with the first stream.

The liquid composition is described the same as above.

ClO₂ ⁰ may be provided from any suitable methods. In certainembodiments, ClO₂ ⁰ is produced from NaClO₂ by an electrochemicalmethod. In another embodiment, ClO₂ ⁰ is produced from a chemicalmethod. In another embodiment, ClO₂ ⁰ is produced in a liquidcomposition. In certain embodiments the reaction products obtained fromthe production of ClO₂ ⁰ can be used in another portion of the methodsdisclosed herein.

ClO₂ ⁰ may be unstable and explosive under certain circumstances. ClO₂ ⁰may be generated in situ to avoid further transportation. The stabilityof ClO₂ ⁰ depends on three primary parameters: temperature, pressure andconcentration. In general, ClO₂ ⁰ is less stable at a highertemperature, higher pressure and/or higher concentration. There are anumber of safe operating environments for ClO₂ ⁰. Tables (1) and (2)depict the safe working environments and environments that promotedecomposition characteristics of ClO₂ ⁰. With good abatement equipmentdesign that effectively maintains temperatures, pressures and ClO₂ ⁰concentrations within the desired parameters, it is possible to treatthe first stream having a NO_(x) concentration of about 40,000 ppmV orless, about 50,000 ppmV or less, or about 60,000 ppmV at a temperatureat or below about 38° C. using reactions (3) and (4) within the stableClO₂ ⁰ gas phase parameters outlined in Tables (1) and (2). With goodabatement equipment design that minimizes reaction residence times andeffectively maintains temperatures, pressures and ClO₂ ⁰ concentrationswithin the desired parameters, it is possible to treat the first gasstreams at a temperature at or below about 80° C. using reactions (3)and (4), even though this temperature is not within the area identifiedas safe in FIG. 2. This is possible because with proper abatementequipment design, reactions (3) and (4) may be completed beforesignificant amount of ClO₂ ⁰ begins decomposition.

Because ClO₂ ⁰ can be unstable, it is desired to generate ClO₂ ⁰ on siteby a suitable means. Furthermore, a short distance between the source ofClO₂ ⁰ generation and its use in the reaction chamber is desired suchthat a short transportation time (e.g. about 1 minute or less, about 30seconds or less, or about 10 seconds or less) is preferred to insurethat ClO₂ ⁰ reaches the reaction chamber and completes the reactionbefore reaching the decomposition time outlined in FIG. 2. As describedabove, the conversion of NO_(x) to the one or more mineral acids and/orsalts thereof can be substantially complete in about 1.5 seconds orless, or 0.15 seconds in the methods disclosed herein.

In certain embodiments, as a reference, a 10% ClO₂ ⁰ concentration in agas composition in FIG. 1 corresponds to a partial pressure of 76 mm Hgin FIG. 2, which is outside of the safe working environment. A 5% ClO₂ ⁰concentration in a gas composition in FIG. 1 is well within the safeworking environment according to FIG. 2. FIG. 1 shows that ClO₂ ⁰ istheoretically safe at up to 9.55% (95,500 ppmV) in a gas compositionwhen used in environments optimized for minimum ClO₂ ⁰ decomposition.

FIG. 3 shows that the safe concentration of ClO₂ ⁰ in an aqueoussolution varies with temperature. For example, thousands of gallons ofClO₂ ⁰ adsorbed, suspended and/or dissolved in water at a concentrationof about 9,000 ppmV can be stored safely at near freezing temperature.ClO₂ ⁰ may be safe for transportation and general storage at aconcentration of about 3,000 ppmV at or below about 30° C. However, thesafe concentration of ClO₂ ⁰ in water at 40° C. is about 2,200 ppmV.Furthermore, other conditions including, without limitation, sunlightand vibrations also may affect the ClO₂ ⁰ stability in aqueous solution.

In certain embodiments, the adsorbed, suspended and/or dissolved ClO₂ ⁰concentration in the aqueous solution is about 4,000 ppmV or lower,about 3,000 ppmV or lower, or about 2,000 ppmV or lower. In certainembodiments, the aqueous solution is a basic aqueous solution with a pHof about 9 or above. In certain embodiments, the method furthercomprises determining the amount/rate of ClO₂ ⁰ addition in the secondstream based on the concentration of NO_(x) in the first stream.

To ensure the conversion of NO_(x) to one or more mineral acids and/orsalts thereof occurs at a desired removal efficiency, the amount of ClO₂⁰ used can be above the stoichiometric amount based on reactions (3) and(4) (e.g. about 10% to about 20% higher). In certain embodiments, themethod further comprises determining the NO and/or NO₂ concentration(s)in the first stream before and/or after the first stream contacting thesecond stream and leaving the reaction chamber; then determining thestoichiometric amount of ClO₂ ⁰ needed in the second stream; andoptionally determining the ClO₂ ⁰ concentration in the stream leavingthe reaction chamber before determining the stoichiometric amount ofClO₂ ⁰ needed in the second stream. In certain embodiments, the methodfurther comprises determining the NO_(x) concentration in the firststream after contacted with the second stream and/or the pH of theliquid condensate formed as a result of first and second stream mixingto determine the amount of ClO₂ ⁰ and/or the basic aqueous solutionneeded in the second stream.

In certain embodiments, the second stream further comprises ClO₂ ⁰ gaswhen the NO_(x) concentration in the first stream requires more ClO₂ ⁰than can be safely adsorbed, suspended and/or dissolved into an aqueoussolution, or when the humidity of the second stream precludes theaddition of more aqueous solution containing ClO₂ ⁰ gas without causingcondensation within the reaction chamber.

In certain embodiments, when the ambient relative humidity is notsufficient, the method further comprises spraying, releasing orpropelling finely atomized mist of water or an aqueous solution at apoint upstream of the ClO₂ ⁰ addition.

In certain embodiments, the method further comprises contacting thetreated first stream within the reaction chamber or in another reactionchamber after the treated first steam leaves the reaction chamber withanother stream to enhance the capture of hydrochloric acid, nitric acid,other mineral acids, and/or ClO₂ ⁰. Examples of such stream include,without limitation, an aqueous solution (e.g. basic, acidic, neutral orsubstantially neutral). In certain examples when the desired finalproducts are salts of the mineral acids (e.g. hydrochloric acid andnitric acid), the other stream comprises the corresponding basic aqueoussolution to form the desired salts thereof. In certain examples when thedesired final products are the mineral acids (e.g. hydrochloric acid andnitric acid), the other stream comprises an acidic or substantiallyneutral aqueous solution.

In another embodiment, a method of removing atmospheric pollutioncompounds from a waste gas stream disclosed herein include: providing asingle-stage air scrubbing apparatus, providing a waste gas stream (afirst stream) having at least one atmospheric pollution compound (e.g.one or more oxides of nitrogen and/or one or more oxides of sulfur),providing at least one additional gas stream, mist stream, liquid streamor combination thereof (a second stream), introducing the first streamand the second stream into the single-stage air scrubbing apparatus at aflow rate and retention time in the reaction vessel that is sufficientto allow for conversion of at least one atmospheric pollution compoundin a gas phase reaction.

Second Method: Two-Stage Conversion of NO_(x) to MNO₂

Another aspect of the invention relates to a second method comprising:

(2a) contacting a first stream comprising NO and/or NO₂ with a secondstream comprising ClO₂ ⁰ to provide a third stream comprising NO and NO₂at a molar ratio of about 1:1; and

(2b) contacting the third stream with a fourth stream comprising anaqueous metal hydroxide (MOH) solution to convert NO and NO₂ to MNO₂.

In one embodiment, the metal hydroxide MOH is NaOH, and the reactioninvolved in step 2b includes, without limitation, reaction (6):

NO+NO₂+2NaOH→2NaNO₂+H₂O  (6)

Similar reactions are involved when the metal hydroxide is a differentmetal hydroxide. Examples of MOH are the same as described supra withrespect to the first method.

The first stream and the second stream in step 2a can be the same asdescribed supra with respect to the first method, except that therate/amount of ClO₂ ⁰ in the second stream is provided to obtain theabout 1:1 molar ratio of NO/NO₂ in the third stream. The ClO₂ ⁰ in thesecond stream can react with NO and/or NO₂ via reactions (3) and/or (4).Although both reactions (3) and (4) are fast reactions, the rate ofreaction (3) is significantly faster than that of reaction (4). Thus,the relative concentration of NO and NO₂ can be adjusted by adding justenough ClO₂ ⁰ to preferably convert NO to NO₂ (reaction (3)) while notenough to further convert NO₂ to nitric acid and/or salts thereof(reaction (4)).

In another embodiment, the method further comprises determining theconcentrations of NO and NO₂ in the first stream before contacting thesecond stream and using this information to determine the requiredaddition of ClO₂ ⁰ to the second stream that will produce about 1:1molar ratio of NO/NO₂ in the resultant third stream. In certainembodiments, the amount of ClO₂ ⁰ used is above the stoichiometricamount based on reaction (3) (e.g. about 10% to about 20% higher).

In another embodiment, the method further comprises determining theconcentrations of NO and NO₂ in the third stream after the contactingand mixing of the first and the second streams. This concentrationinformation is used to determine the required addition of ClO₂ ⁰ to thesecond stream that will produce about 1:1 molar ratio of NO/NO₂ in theresultant third stream.

In another embodiment, the aqueous metal hydroxide (MOH) solution ofstep (2b) further comprises one or more oxidants to further facilitatethe desired conversion. Examples of such oxidants include, withoutlimitation, NaOCl, NaClO₂, NaClO₃, H₂O₂, KMnO₄, and combinationsthereof. In certain examples, the amount of the total oxidant(s) isabout 2% to about 6% by weight of the aqueous metal hydroxide (MOH)solution.

In another embodiment, the fourth stream of step (2b) comprises theaqueous metal hydroxide (MOH) solution and one or more oxidantsdescribed supra. In one example, the fourth stream is provided byspraying, releasing, or propelling the aqueous metal hydroxide (MOH)solution and the one or more oxidants. In another example, the aqueousmetal hydroxide (MOH) solution and the one or more oxidants are mixedbefore the spraying, releasing or propelling. In another example, theaqueous metal hydroxide (MOH) solution and the one or more oxidants arenot mixed before the spraying, releasing or propelling. In anotherexample, the mist stream has a mean diameter of about 200 microns orlower, or about 100 microns or lower. The mist droplets can be generatedusing any droplet forming technology as described supra with respect tothe first method.

The method described herein uses ClO₂ ⁰ to convert excess NO to NO₂, anduses the less expensive and easier to handle chemical, the aqueous metalhydroxide (MOH) solutions (e.g. NaOH aqueous solution), to furthercomplete the conversion of NO and NO₂ to an innocuous compound (e.g.NaNO₂). Furthermore, the NaNO₂ produced from the method can be furtherpurified as a commercial chemical product.

The required contacting time of the first stream and the second streamof the second method is about the same or shorter compared to thatrequired in the first method. The handling considerations of ClO₂ ⁰ inthe second method are the same as those described in the first method.The concentration ranges of ClO₂ ⁰ suitable for the second method areabout the same or lower than those suitable for the first method.

Furthermore, when ClO₂ ⁰ is generated using an electrochemical device,the effluent from the cells can be utilized in the second scrubbingstage to minimize the addition of NaOH in step (2b).

In another embodiment, a method of removing atmospheric pollutioncompounds from a waste gas steam disclosed herein comprises: providing atwo-stage air scrubbing apparatus, providing a waste gas stream (a firststream) having at least one atmospheric pollution compound (e.g. one ormore oxides of nitrogen and/or one or more oxides of sulfur), providingat least one additional gas stream, mist stream, liquid stream orcombination thereof (a second stream/a fourth stream) into each stage ofthe air scrubbing apparatus at a flow rate and retention time in eachreaction vessel that is sufficient to allow for conversion of at leastone atmospheric pollution compound into another innocuous nitrogen orsulfur containing compound.

In another embodiment, a method of removing atmospheric pollutioncompounds from a waste gas stream disclosed herein comprises: providinga two-stage air scrubbing apparatus, providing a waste gas stream (afirst stream) having at least one atmospheric pollution compound (e.g.one or more oxides of nitrogen and/or one or more oxides of sulfur),providing at least two additional gas streams, mist streams, liquidstreams or combination thereof (a second stream and a fourth stream),introducing the first stream and the second and fourth streams into thetwo-stage air scrubbing apparatus at a flow rate and retention time inthe reaction vessels that are sufficient to allow for conversion of atleast one atmospheric pollution compound.

Advantages of the Methods Disclosed Herein

The methods disclosed herein treat NO_(x) more efficiently and withlower initial equipment/operating costs than the prior art processes.The methods disclosed herein provide unexpected improvements in thetreatment of industrially created NO_(x) waste gas with unexpectedlyshort treating time, unexpectedly high throughput and unexpectedly highefficiency.

The gas phase reactions described in equations (3) and (4) herein arefaster than the liquid phase reactions described by Lee et al. in U.S.Pat. No. 7,455,820. The reactions disclosed by the Lee reference areslower and less efficient than the reactions described herein becausethe Lee reference's reactions require the sparingly soluble NO and themoderately soluble NO₂ in the NOx to undergo gas/liquid phase masstransfer within a liquid phase which slows down the conversion of NOxinto reaction products. The rate limiting mass transfer required in theLee reference is not required in reactions described in equations (3)and (4) of the instant invention because the novel reactions between NO,NO₂, and SO₂ with ClO₂ ⁰ in this disclosure occur in gas phase.

The methods disclosed herein are applicable to industrial applicationsincluding, without limitation, chemically dissolving and picklingmetals, stationary source combustion process flue gas, tail gas fromnitric acid plants, shipboard combustion process flue gas and othersources of waste gas containing one or more oxides of nitrogen.

In addition, the apparatus described in for use with the presentinvention comprises a single stage gas/mist scrubbing apparatus that isa major departure from the conventional multi stage wet scrubbingapparatus or the liquid phase bubble reactor described by the Leereference.

Apparatus Used in the Methods Disclosed Herein

Another aspect of the invention relates to an apparatus that can be usedin the methods disclosed herein.

In one embodiment, the apparatus comprises a single-stage air/mistscrubbing apparatus that is a major departure from the conventionalmulti-stage wet scrubbing apparatus.

Specifically, the single-stage air/mist scrubbing apparatus is used forthe contact/reaction of ClO₂ ⁰ with NO and/or NO₂. Such apparatus mayalso be used at the first stage in the two-stage methods disclosedherein. The single-stage air/mist scrubbing apparatus comprises: areaction vessel having a first end, a second end, an enclosure, at leastone wall, a volume within the enclosure and a residence time component,at least one introduction duct coupled to the reaction vessel, and aturbulence component; wherein the residence time component is sufficientto allow the substantial completion of the desired conversion of NOand/or NO₂ (e.g. about 95% or higher conversion, about 98% or higherconversion, or about 99% or higher conversion) of the desired conversionof NO to one or more mineral acids and/or salts thereof, or NO to NO₂ sothat the resultant stream has about 1:1 molar ratio of NO/NO₂).Unexpectedly, a short residence time (the contact time) is needed toaccomplish this conversion. For example, the residence time (the contacttime) can be about 1.5 seconds or shorter, or about 0.15 seconds orshorter when the first and the second streams are thoroughly mixed.

The reaction vessels may be constructed of materials that are imperviousto the first stream and have a volume sufficient to contain the firststream for a period of time that is not less than the residence time(e.g. about 1.5 seconds or shorter when ClO₂ ⁰ gas is adsorbed,suspended or dissolved in a liquid/mist stream and the liquid/miststream is introduced into the reaction vessel via an atomizer, about0.15 seconds or shorter when ClO₂ ⁰ is introduced in a gas stream) whenthe mixing of the first and the second streams is sufficient. Thereaction vessel may be any shape and comprise at least one wall. Incertain embodiments, the reaction vessel is cylindrical (i.e. having acircular cross-section profile) because this shape minimizesinterference between the first stream and the vessel wall(s). However,when the first and the second streams are gas streams, or when the firststream is a gas stream and the second stream contains very small liquiddroplets (e.g. having a mean diameter of about 200 microns or lower, orabout 100 microns or lower), any shape of the reaction vessel thatallows the mixing of the first and second streams with minimalcoalescing of droplets to form moisture within the reaction chamber iscontemplated, even if it is not cylindrical. In certain embodiments, noliquid droplets or moisture forms. However, these components should bedesigned to withstand and address different types of the first stream,treatment conditions and resulting components. Therefore, if thereaction chamber can provide sufficient residence time, along with alack of moisture coalescence, any design may be used, including withoutlimitation, rectangular, oval, triangular, conical and combinationsthereof.

The first stream is introduced to the reaction vessel through the atleast one introduction duct coupled to the reaction vessel. For optimumperformance, it is desired to design the orientation of the duct tominimize the interference between the gas and the vessel walls. Examplesof such optimized orientations for a cylindrical reaction vesselinclude, without limitation: a) at the center of the end of thecylindrical reaction vessel, and b) at the side and tangentially alignedwith circumference of the reaction cylindrical vessel.

The turbulence component may comprise any design or combinations thereofto introduce stream mixing by providing a swirl or turbulence to anystream involved in the method, (e.g. the first stream, the secondstream, any component gas/stream thereof; e.g. the

ClO₂ ⁰ gas stream, the aqueous stream containing ClO₂°, or anycombinations thereof). In certain embodiments, the turbulence componentis located such that it can add turbulence or mixing to the streamsbefore contacting ClO₂ ⁰ gas or ClO₂ ⁰ adsorbed, suspended and/ordissolved in a mist or liquid. When ClO₂ ⁰ is introduced as a gas themixing can occur before or after the ClO₂ ⁰ is introduced in the secondstream, or before or after the ClO₂ ⁰ is added to the first streamcontaining NO_(x).

In certain embodiments, when the first stream is introduced at thecenter of the end of a cylindrical reaction vessel, the turbulencecomponent is placed in the duct just prior to the point where the firststream enters the reaction vessel or at the beginning of the reactionvessel just after the first stream enters the vessel. Alternatively, thereaction can occur in a duct without a reaction vessel and theturbulence component is placed in the duct. In certain embodiments, whenthe first stream is introduced at the side and tangentially aligned withcircumference of a cylindrical reaction vessel, the turbulence componentcan be located at a position to swirl or mix the gas/stream in the ductjust prior to the point where the first stream enters the vessel. Incertain embodiments, a rectangular or other reaction vesselconfiguration is used, and the turbulence component is designed in orderto minimize the collision between the vessel walls and the gas/streamturbulence within the reaction vessel when ClO₂ ⁰ is introduced in amist or liquid phase.

The requirement for a vessel volume is associated with the methodologyof introducing ClO₂ ⁰ into the second stream. When the ClO₂ ⁰ is presentas a gas, the residence time is about 0.15 seconds or less when streammixing is sufficient. When ClO₂ ⁰ is adsorbed, suspended and/ordissolved in a liquid then the residence time is longer, e.g. about 1.5seconds of residence time with a good mixing between the first and thesecond streams.

In certain embodiments, ClO₂ ⁰ is adsorbed, suspended and/or dissolvedin a liquid to form the second stream. The second stream is sprayed,released or propelled into the first stream. In certain embodiments, thesecond stream is sprayed, released or propelled at a point justdownstream of the point at which the first stream is swirled by theturbulence component, through a single or multiple nozzles. In certainexamples, it may also be beneficial for the first stream nozzle(s) tospin in opposite directions of the second stream nozzle(s).

In certain embodiments, the nozzle orientation is centered with the axisof the stream flow and provides a full cone or other full surfacepattern that evenly disperses the material projected from the nozzleinto the entire stream. In certain embodiments, the rate of release fromthe nozzle may be calibrated so that it is at least twice the velocityof the stream. When the nozzle is emitting a liquid, it preferablyproduces droplets of that liquid with a mean diameter of about 100microns or less, or about 200 microns or less. In these instances, it isimportant to remain below the dew point of the gas, and thereby preventformation of liquid droplets, especially those with a larger diameter.

Liquid may be formed from a condensed spray in the reaction, but mayalso be formed from other methods and/or apparatus. Such liquid maycontain high concentrations of HCl and HNO₃. In certain embodiments, thereaction vessels further comprises a drain at a low point in the vesselto allow the removal of such liquid. In certain embodiments, dependingupon other contaminants in the first stream and the pH of the condensedmoisture (fluid material) added to the first stream, this condensateacid mix can be of commercial value.

In certain embodiments, the ClO₂ ⁰ gas is generated on site andintroduced (e.g. sprayed) into the first stream through the nozzledescribed above, as a liquid or mist stream and/or a gas stream.

In certain embodiments, the rate of ClO₂ ⁰ addition is based on theconcentration of NO_(x) in the first stream. In certain embodiments, theNO_(x) concentration is not consistent in the first stream. Theapparatus further comprises automated chemical feed controls to optimizeboth removal efficiency and scrubber operating costs. An example of theautomated chemical feed controls is described in Example 4. Theautomated feed controls are designed to detect the NO and NO₂concentration in the untreated first stream, or the NO, NO₂ and ClO₂ ⁰concentration at the effluent of the reaction vessel, at a point in theducting past the reaction chamber, and/or at a point on the exhauststack. Other control inputs include, without limitation, pressure, flow,concentration, pH and temperature for various components in the process.

In certain embodiments, the apparatus further comprises a blower topush/pull the first stream into the reaction vessel. The blower can beplaced before or after the reaction vessel (upstream or downstream ofthe reaction vessel). In some embodiments, the blower is placeddownstream (after) of the reaction vessel. Such placement keeps theducting and reaction vessel at slightly negative pressure when comparedto the atmosphere, and therefore eliminates the release of untreatedfirst stream in the event of a leak. The downstream orientation can alsobe advantageous because it reduces the pressure in the reaction systemslightly below ambient. The lower working pressure enhances the safeworking environment for ClO₂ ⁰ gas. Furthermore, the blower may have avariable frequency drive with enhanced operational flexibilities. Insome embodiments, the air flow through the ventilation system includingthe reaction vessel may be reduced in volume during the hours whenNO_(x) is not actively generated. This feature is designed to maintain aminimal air exchange in the areas that create the waste gas.

In certain embodiments, the apparatus may further comprise a second mistor packed bed scrubbing apparatus to improve the decontaminated gasquality while enhancing the capture of the mineral acids generated fromthe process (e.g. HCl and HNO₃).

In certain embodiments, when the apparatus is used for the second methoddisclosed herein, the apparatus further comprises an apparatus tocomplete the step (2b). Known apparatus can be adapted to complete thestep (2b) in the methods disclosed herein. Such apparatus include, butare not limited to, co-current packed bed scrubbers, atomizes mistscrubbers, concurrent packed bed scrubbers, horizontal flow packed bedscrubbers and bubble or tray type scrubbers. In certain embodiments, thesystem according to the present invention further comprises a firststage scrubber upstream from the reaction vessel, wherein waste gas fromthe first stage, acid fumes, and low or no nitrogen oxides are treatedin the reaction vessel.

In any of the above embodiments, the same or similar principles may beapplied for the treatment of one or more oxides of sulfur.Sulfur-containing compound will not interfere with the methods disclosedherein.

EXAMPLES Example 1 Single Stage Scrubbing Method

An embodiment of the first method disclosed herein is demonstrated inthis example using a single-stage pilot scale mist scrubber. The pilotscrubber processes a slip stream of waste gas at approximately 22° C.from a chemical milling operation. The NO_(x) concentration in the wastegas stream varies between 10 and 200 ppmV during the series of testscompleted to test this new process methodology. However, it should beunderstood that significantly high concentrations of NO_(x) can betreated in a waste gas stream, including concentrations of 40,000 ppmVor more. The NO/NO₂ ratios in the NO_(x) may vary slightly, and the NOconcentration in the NO_(x) can be consistently above 90%.

FIG. 4 shows a section cut through a contemplated embodiment—thesingle-stage pilot scrubber—that can be used in the performance testing.A scrubber vessel (10) is a PVC pipe mounted horizontally duringtesting. The vessel (10) in any other configuration and orientation thatcan provide an enclosure for mist is applicable and included in thisdescription. Waste gas (the first stream) enters the vessel (10) throughthe PVC pipe (11). A PVC baffle plate (12) disturbs the first streamflow linearity in the vessel (10) prior to a stream swirling device(13). An air atomized nozzle (nozzle) (14) is used in the tests tointroduce the second stream to the first stream in the vessel (10). Insome tests, the nozzle (14) is used to introduce the second stream as aliquid stream that continues through a tube (15). In other tests, thesecond stream contains only gas and is introduced to the nozzle througha tube (16). The pressure and flow rate of the stream fed to the nozzle(14) are adjusted at a regulator (17). A hole (20) is used to extracttreated stream samples from the vessel (10). The hole (20) is repeatedin the vessel (10) at intervals away from the nozzle (14) so thatsamples with progressively longer residence time in the vessel (10) canbe obtained and analyzed to determine the rate of NO_(x) destruction inthe stream within the vessel (10). The rate of NO_(x) destruction in thevessel (10) is determined by comparing the treated stream samples fromthe various hole (20) locations against untreated waste gas samplestakes at a hole (21). The first stream is moved through the vessel (10)by ducting (22) connected to the suction side of a variable flow rateblower.

The contemplated processes, as outlined earlier, utilize two methods (asdescribed in steps 1a and 1b) in which ClO₂ ⁰ effectively converts gascontaining both NO and NO₂ into one or more mineral acids (e.g. HNO₃)and/or salts thereof in a single-stage mist type gas scrubbingapparatus. The method described in step 1a includes a reaction between agas containing NO_(x) and ClO₂ ⁰ adsorbed, suspended and/or dissolved ina basic solution. The method described in step 1b includes a reaction ofa gas with high relative humidity containing NO_(x) and ClO₂ ⁰. Bothmethods involve reactions (3) and (4) as described supra.

5NO+2ClO₂+H₂O→5NO₂+2HCl  (3)

5NO₂+ClO₂+3H₂O→5HNO₃+HCl  (4)

Both methods using a single-stage mist scrubbing apparatus are a majordeparture from the multi-stage wet scrubbing apparatus reported in priorart.

Greater than 99% removal efficiency of NO_(x) is accomplished in lessthan 1.5 seconds when the humid gas containing NO_(x) and ClO₂ ⁰ is wellmixed.

An optional second stage mist or wet scrubbing apparatus can provideseveral functions. First, it removes excess ClO₂ ⁰ in the apparatus.This is especially helpful for apparatus without automated controls toeffectively regulate ClO₂ ⁰ gas addition. Second, it captures HCl, HNO₃acid fumes.

Reactions (3) and (4) occur more rapidly in the mist and gas phasescrubbing technology than the wet scrubbing reactions described inreactions (1) and (2). The increased speed of reaction reduces thereaction vessel size required for conversion of NO_(x) to the one ormore mineral acids or salts thereof. Furthermore, the gas or mistscrubbing methodology using ClO₂ ⁰ as described in reactions (3) and (4)is less complicated and requires less maintenance than the packed bed ortray type wet scrubbers that utilize reactions (1) and (2). As a result,the air or mist technology equipment is less expensive to purchase andoperate.

Stream analysis for NO and NO₂ was done during the pilot testing usingelectrochemical sensors for NO and NO₂. These sensors are evaluated forcross sensitivities by other compounds known or suspected to be in thestream. The sensors are also factory calibrated before and aftertesting. The electrochemical analysis is further cross checked with EPAMethod 07 for NO_(x).

Example 2 Two Stage Scrubbing Methodology

FIG. 5 shows a possible flow diagram for a two-stage scrubbing method asdescribed herein. The reaction chambers of the two stages are connected(107: the first-stage reaction chamber; and 109 or 112: the second-stagereaction chamber options). Known mechanical methodology, equipment andprocesses can be adapted to the methods disclosed herein for use in thesecond stage of the two-stage methodology set forth herein. Theseinclude, but are not limited to, co-current packed bed scrubbers,atomizes mist scrubbers, concurrent packed bed scrubbers, horizontalflow packed bed scrubbers and bubble or tray type scrubbers and methodsrelating to the same. In one embodiment, a full scale application of themethods described herein utilizes the packed bed option (109) as shownas the second stage option in FIG. 5. Referring to FIG. 5, air pulledthrough an exhaust hood or other device of any configuration (100)contains NO from industrial or combustion processes. Ducting (101) canbe made of any material that is compatible with the gases that itconducts between the source of the NO containing air and the first stagereaction chamber (107).

On-site production of ClO₂ ⁰: There are a number of effective ClO₂ ⁰generation technologies, but most are limited to only producing the ClO₂⁰ gas adsorbed, suspended or dissolved in a liquid. The gas phase ClO₂ ⁰can be produced by including a separate gas stripping technology.Electrochemical generation (102) can provide both gas phase ClO₂ ⁰ andClO₂ ⁰ adsorbed, suspended or dissolved in a liquid. Each method of ClO₂⁰ generation requires its own requisite chemicals provided by (103).Waste products from ClO₂ ⁰ gas generation vary according to themethodology used. The generation of ClO₂ ⁰ gas by an electrochemicalmethodology produces waste byproducts including NaOH, NaClO₂, and NaClO₃in solution. These are utilized in the second stage scrubbing andtherefore reduce the need for additional NaOH and other chemicalsdescribed in (110) or (113). Other chemical methods of generating ClO₂ ⁰gas produce waste byproducts that are not useful in the second stagescrubbing and therefore must be treated as hazardous waste at anadditional operating cost (104). The ClO₂ ⁰ gas is generally transferredunder slight vacuum to the reaction chambers (107). The slight vacuum isgenerated because the blower/fan (115) that moves the NO contaminatedair (the first stream) from its source (100) to the stack (116) isgenerally located after the second-stage scrubber (109 or 112). Thisplacement insures the entire air handling system up to the fan/blower(115) is at a negative pressure with respect to atmospheric pressure.The tube (105) used to transfer the ClO₂ ⁰ gas from the generator to thefirst-stage reaction chamber (107) is made from a material that isimpervious to ClO₂. For ClO₂ ⁰ gas safety reasons, this tube (105) is asshort as possible. The efficiencies of reactions (3) and (4) aredependent on good mixing of the streams. The details of mixingtechnology and placement of the mixing device (106) with respect to theintroduction of the second stream to the first-stage reaction chamber(107) of the scrubber or the fourth stream to a second-stage reactionchamber (112) of the scrubber are described elsewhere in this report.The first stage reaction chamber (107) is made of materials that arecompatible with the gases being treated. The chamber volume, shape andorientation are described herein. The purpose of the chamber is toprovide a sufficient volume of a confined space for the production ofthe desired reaction product. In a two-stage scrubbing method, thefirst-stage reaction provides 1:1 molar ratio of NO and NO₂. This volumeof the reaction chamber (107) provides sufficient residence time forreaction (3) to reach the desired end point. The second-stage reactionchamber can utilize several conventional methodologies in novel ways asdescribed herein. These conventional methodologies include, but are notlimited to, counter current packed bed scrubber and aerosol mistreaction chamber. In FIG. 5, (108) means a choice can be made for thesystem to use either a packed bed scrubber (109) as the second-stagereaction chamber (109), or alternatively, an aerosol mist reactionchamber as the second-stage reaction chamber (112). Counter currentpacked bed scrubber methodology is documented in literature but thisparticular application of the technology is novel when a packed bedscrubber (109) is used to remove both NO and NO₂ in about 1:1 molarratio with the methods described herein. The chemical mixture (110) thatfacilitates 1:1 molar conversion of NO and NO₂ into NaNO₂ as describedin reaction (6) are NaOH, with one or more oxidizers e.g. NaClO₂ and/orClO₂ and/or NaClO₃ and/or NaOCl and/or H₂O₂. Each of these oxidizersenhances the extent to which the NO and NO₂ are transformed into thedesired compounds. A recirculation pump (111) is typically a part of thepacked bed scrubber technology. This pump (111) transfers a liquid thatcan be H₂O optionally containing the chemicals as described supra in(110) from the scrubber sump to a point above the scrubber packingbed(s) in order to keep the packing material wetted. The chemicalreactions between NO_(x), NaOH and the other chemicals as described initem (110) occur in the film layer surrounding the surface of each pieceof packing in (109).

Alternatively, mist or atomized droplets may be used in an aerosol mistreaction chamber (112) to scrub airborne contaminants as commonly usedfor the conversion of hydrogen sulfide and other sulfur containingcompounds, but it is novel for the conversion of NO_(x) (NO and NO₂)according to reaction (6) in an aerosol mist reaction chamber as thesecond-stage reaction chamber (112). This reaction chamber (112) is madeof materials that are compatible with the chemicals it will be exposedto. The reaction chamber (112) is sized to provide the residence timenecessary for completion of the reaction (6) to the level of removalefficiency required. Longer residence time results in higher removalefficiency. Additional information on the second-stage reaction chamber(112) is described herein. Chemicals utilized in the aerosol mistreaction chamber are provided from item (113) and are the same as thoseidentified in item (110) above. The method of introduction of the fourthstream to the second-stage reaction chamber (112) is dramaticallydifferent from that in the packed bed scrubber (109). The chemicalsdescribed in (110) are added to the sump of the packed bed scrubber(109) and transferred to a wet film on the packing within the packed bedscrubber (109). In the aerosol mist reaction chamber (112) the chemicalsdescribed in (110) are introduced in a mist with a mean diameter ofabout 100 microns or a mean diameter of about 200 microns. The mist ismade by a variety of means including air atomized nozzles, anddiametrically opposed gas/liquid stream impingement nozzles and sonicnozzles in various configurations. The shape of the reaction chamber(112) and nozzle(s) orientations are configured in ways that optimizeinteraction between the streams while minimizing the coalescing ofdroplets within the reaction chamber (112). Ducting (114) is similar tothat described in item (101). The fan/blower (115) is typically locatedafter the reaction chambers. This orientation insures the entire airhandling system from (100) up to the fan (115) is at a slightly negativepressure when compared to the atmosphere. This orientation enhances thesafety of ClO₂ ⁰ in the first-stage reaction chamber and also insuresthat any leak in the mechanical system will entrain ambient air ratherthan discharge contaminated air into the atmosphere. The blower/fan(115) is made from materials that are compatible with the chemical inthe air stream and sized to accommodate the site specific differentialpressure and gas flow requirements. An exhaust stack (116) is designedto meet regulatory compliance requirements for dispersion modeling andother parameters. The stack (116) is made from materials that arecompatible with the gas that passes through it. Clean air (117) is arelative term that is mandated by local regulatory agencies. Thisprocess addresses NO_(x) abatement issues and has the propensity to meetremoval efficiencies of about 95% or more, about 98% or more, about 99%or more. The exit arrow (117) represents clean air. This process has theability to create differences in NO_(x) removal efficiency throughdifferences in the design of the equipment. The differences in equipmentdesign include but are not limited to reaction vessel residence times,gas mixing, nozzle types and placement and chemical dosing.

There are advantages to the selection of an electrochemical method ofClO₂ ⁰ generation. The equipment cost of electrochemical generation ishigher than two and three chemical methods of ClO₂ ⁰ generation, but allor part of this difference is offset by the cost of gas strippingtechnology necessary to produce the requisite gas phase ClO₂ ⁰ used inthe NO_(x) process associated with reactions (3) and (4). Theelectrochemical equipment cost differential is often outweighed by theadvantages of lower costs associated with disposing of chemical wasteproducts associated with ClO₂ ⁰ generation. Almost no chemical waste isproduced with the electrochemical generation process because thereaction byproducts include sodium hydroxide and are utilized in thesecond-stage scrubber. The chemical waste produced from other ClO₂ ⁰generation processes may not be reused in the second-stage scrubbing.

Example 3 Forms of ClO₂ ⁰ Introduction

ClO₂ ⁰ was introduced to the stream comprising NO_(x) by three ways: ina gas stream, in a mist stream or in a liquid stream. These threemethods used the same stoichiometry, because it is ClO₂ ⁰ that reactedwith NO_(x), and not the ClO₂ ¹ anion. Moreover, regardless of themethod of introduction of the ClO₂ ⁰, the reaction occurred withgas-phase ClO₂ ⁰ which was either introduced into the reaction vessel inthe gas phase or which evaporated upon introduction by an atomizer andprior to contacting the first stream. Thus, the methods disclosed hereinwere significantly different from the wet scrubbing of NO using the ClO₂⁻ anion to react with NO_(x).

Mechanical Configuration:

The gas and mist stream systems have different mechanicalconfigurations: different nozzle types, different sequences of mixing,and different phases for ClO₂ ⁰ transportation into the reactionchamber. In the gas stream, mixing after the gas injection worked betterthan the opposite sequence. In the mist stream systems, in certainexamples, the issue of droplet aggregation superseded this mixingadvantage because mixing after the gas injection tended to cause dropletagglomeration. Therefore mixing was and is introduced prior to ClO₂ ⁰addition when the mist stream is used.

Mist Stream:

Mist stream was initially developed for operations with modest waste gasflow rates (the first stream) and modest NO_(x) concentrations in thewaste gas. This method is cost effective for a first stream flow ratesof about 10,000 CFM or less and NO_(x) concentrations of about 1,000ppmV or less. Subsequent studies revealed that this methodology isapplicable to larger waste gas flow rates and NO_(x) concentrations.

This process is also cost effective for smaller applications. ClO₂ ⁰ wassupplied in the form as adsorbed, suspension and/or dissolved in aliquid composition (e.g. an aqueous solution buffered to minimizeoff-gassing so that the cost of onsite ClO₂ ⁰ generation was no longerneeded). Applications involving larger waste gas flow rates are costeffective when onsite ClO₂ ⁰ generation is used.

Liquid containing ClO₂ ⁰ is commercially available up to about 3,000ppmV ClO₂ ⁰. A 3,000 ppmV solution was the maximum concentrationconsidered stable for transport. Higher concentrations up to about19,000 ppmV are possible when ClO₂ ⁰ is generated on site at fixedlocations and stored in liquid that is maintained at a lower temperature(see FIG. 3 for details).

Gas Stream:

Industrial waste gas streams (the first stream) of a wide range ofvolumes and NO_(x) concentrations were effectively treated when thesecond stream containing ClO₂ ⁰ was a gas stream and introduced into thefirst stream before the mixture was further mixed. This applicationrequired onsite generation of ClO₂ ⁰ gas and was therefore moreeconomically cost effective when the first stream was in excess ofapproximately 10,000 CFM and the NO_(x) loading was 50 ppmV or more. Theprocess was and is applicable to NO_(x) loading as high as 60,000 ppmV.This gas stream process was and is at least 10 times faster than themist stream process, as described above. This considerably faster gasphase reaction dramatically reduced the size of the reaction vessel oreven eliminated it completely.

Example 4 An Example of Automated Chemical Feed Controls

An automated control system can be designed and built to monitor,operate and control all of the equipment for any scale application ofthis NO_(x) abatement process utilizing reactions (3) and (4). Thecontrol system can be connected to the following components:

An extensive array of sensors and detectors to monitor processconditions in each aspect of the overall system. Process conditions mayinclude concentrations of one or more sulfur oxides, one or morenitrogen oxides, and/or ClO₂ ⁰ in various process streams.

A generator capable of producing ClO₂ ⁰ in a gas phase or adsorbing,suspending and/or dissolving ClO₂ ⁰ in a liquid composition. In apreferred embodiment, the ClO₂ generator is configured to receive analoginputs from sensors detecting quantities of nitrogen oxides and ClO₂,and the analog inputs are used to regulate a rate of generation of ClO₂by the ClO₂ generator. In some embodiments, the ClO₂ generator furthercomprises a ClO₂ delivery system configured to provide a flow rate ofClO₂ to the inlet for introducing ClO₂, wherein the ClO₂ delivery systemis configured to receive an output from at least one sensor, and whereinthe ClO₂ delivery system is configured to adjust the flow rate of theClO₂ to the inlet for introducing ClO₂ based on the output of thesensor(s).

A single first-stage NO_(x) scrubber using gas and/or mist streamcontaining ClO₂ ⁰ to convert NO_(x) into one or more mineral acids (e.g.nitric acid) and/or salts thereof, and to optionally generate othermolecules.

A second-stage packed bed scrubber, tray tower or mist/gas phasescrubber or other device designed to create a contact and mixing betweenthe waste gas stream and any molecules added to treat NO_(x) and/or themineral acids generated during the first stage process. The second stagecan recirculate a liquid containing, effluent from the ClO₂ ⁰ generator,and other chemical additives described in (110 and 113 above) includingsodium hypochlorite (NaOCl) and hydrogen peroxide (H₂O₂).

A system to strip ClO₂ ⁰ gas stored in an aqueous composition and toinject it into the reaction chamber of the first-stage NO_(x) scrubber(the first-stage reaction chamber (107)). The ClO₂ ⁰ stripped from watercan be used to supplement ClO₂ ⁰ gas being concurrently made by the ClO₂⁰ generator (102) and augment the amount injected into the first-stagereaction chamber (107). The aqueous composition containing ClO₂ ⁰ can bemade by the ClO₂ ⁰ generator during periods when the industrial facilityis not actively generating NO_(x).

Fans, both direct and variable frequency drive.

A storage and packaging system for ClO₂ ⁰ gas stored in an aqueouscomposition (used to optimize the ClO₂ ⁰ generator production by makingClO₂ ⁰ and storing it in an aqueous composition during times of the daywhen NO_(x) was not being produced).

A communication system via internet for remote process monitoring andupgrades. The control systems can also manage the attached equipment inthree modes of operation:

Operating the above equipment during the business hours to treat NO_(x)generated in the industrial applications. During these periods, the ClO₂⁰ generator can produce ClO₂ ⁰ in a gas phase for direct injection intothe first-stage reaction chamber.

When the industrial facility is not operating and therefore notgenerating NO_(x), the ClO₂ ⁰ generator can produce ClO₂ ⁰ gas that isadsorbed, suspended and/or dissolved (i.e., stored) in an aqueouscomposition comprising, for example, deionized water. The obtainedliquid can be used to supplement gas phase ClO₂ ⁰ made by the ClO₂ ⁰generators and thereby provided an augmented amount of NO_(x) than couldhave been provided by the ClO₂ ⁰ generators alone during periods whenNO_(x) is produced by the industrial facility.

Operating the above equipment during the business hours to treat NO_(x)generated in the industrial applications using both ClO₂ ⁰ gas producedby the ClO₂ ⁰ generator and ClO₂ ⁰ gas stripped from aqueous solutionstored on site.

Thus, the specific embodiments and methods of the removal of NO and/orNO₂ from a first stream, including a discussion of related apparatus,processes and uses thereof have been disclosed herein. It should beapparent, however, to those skilled in the art that many moremodifications besides those already described are possible withoutdeparting from the inventive concepts herein. The inventive subjectmatter, therefore, is not to be restricted except in the spirit of thedisclosure herein. Moreover, in interpreting the specification andclaims, all terms should be interpreted in the broadest possible mannerconsistent with the context. In particular, the terms “comprises” and“comprising” should be interpreted as referring to elements, components,or steps in a non-exclusive manner, indicating that the referencedelements, components, or steps may be present, or utilized, or combinedwith other elements, components, or steps that are not expresslyreferenced.

I claim:
 1. A system for scrubbing a waste gas of at least one of nitrogen oxides and sulfur oxides, comprising: an inlet for introducing chlorine dioxide into the reaction vessel; an inlet for introducing waste gas into the reaction vessel, the waste gas containing at least one component selected from the group consisting of a sulfur oxide and a nitrogen oxide; and a reaction vessel, wherein the reaction vessel is equipped with one or more turbulence inducing devices configured for inducing turbulence, wherein the turbulence inducing device is a stationary device.
 2. The system of claim 1, wherein the reaction vessel is a cylindrical reaction vessel, and wherein the turbulence inducing device is placed in a duct just prior to a point where gas enters the vessel.
 3. The system of claim 1, wherein the turbulence inducing device is placed at the beginning of the reaction vessel just after the waste gas enters the reaction vessel.
 4. The system of claim 1, wherein the reaction vessel is a cylindrical reaction vessel, wherein the waste gas is introduced at a side of the cylindrical reaction vessel and tangentially aligned with a circumference of the cylindrical reaction vessel, and wherein the turbulence inducing component is located at a position configured to swirl or mix the gas in a duct just prior to a point where the waste gas enters the vessel.
 5. The system of claim 1, wherein the reaction vessel is a rectangular reaction vessel, and wherein the turbulence inducing component is configured to minimize collision between the vessel walls and gas turbulence within the reaction vessel when chlorine dioxide is introduced in a mist or liquid phase.
 6. The system of claim 1, wherein the chlorine dioxide is dissolved in a liquid and is sprayed, released, or propelled into the waste gas stream at a point just downstream of a point at which gas is swirled by the turbulence component. 